1. Field of the Invention
The present invention relates to a multi-cylinder internal combustion engine, in which at least some of a plurality of cylinders are capable of selectively resting during engine operation under low load.
2. Description of the Background Art
Among multiple-cylinder internal combustion engines, an engine is known in which some of the cylinders selectively rest, or become non-operative, during normal engine operation under certain low-load conditions. In such an engine, a plurality of cylinders are divided into at least two groups. The throttle valve opening of a second (or other) group is set smaller than that of a first group in a low load range, where the throttle valve opening of the first group is less than a predetermined value. A throttle valve control means is provided for ensuring that, when the throttle valve opening of the first group has reached the predetermined value, the throttle valve opening of the second group is thereafter increased at a ratio larger than that for the throttle valve opening of the first group. When the throttle valve opening of the second group coincides with the throttle valve opening of the first group, the throttle valve openings of the first and second groups are thereafter varied at the same rate. Such an engine is disclosed, for example, in Japanese Patent Laid-open No. Hei 07-150982.
In Japanese Patent Laid-open No. Hei 07-150982, the irregular combustion in a 2-cycle engine can be suppressed by the throttle valve control. However, since the cylinders in the second group, which have been at rest, are operated when the throttle valve opening in the first group reaches a predetermined value, a step in engine output is generated at the time of operating the cylinders in the second group.
Accordingly, it is an object of the present invention to provide an internal combustion engine, in which at least some of a plurality of cylinders are capable of selectively resting during engine operation and which can eliminate engine output variations at the time of transition in the number of operable cylinders.